Mandibular Condyle Tissue Reaction to Low Intensity Pulsed Ultrasound in a Young Adult Rat Animal Model

• Author / Creator

  Hadaegh,Yasamin

• Mandibular condyle, especially in postnatal life, grows mainly by endocondral bone growth and has a pivotal role in development of the mandible and oro-facial complex as a whole. This important growth site of the mandible has unique adaptive remodeling in response to external stimuli even beyond natural growth. The mechanical stimulus produced by Low Intensity Pulsed Ultrasound (LIPUS) is osteoinductive and chondroinductive. It has been reported by previous studies that the application of LIPUS on the temporomandibular joint area can enhance mandibular growth in growing individuals. The aim of this thesis was to identify the effect of LIPUS on mandibular condylar remodeling in young adult rats. Nineteen ≈120-day-old female Sprague Dawley rats were allocated to experimental (n=10) and control (n=9) groups. The animals in the experimental group were sonicated bilaterally, 20 minutes each day for 28 consecutive days. The standard setting for LIPUS application used in the present study consisted of a1.5 MHz sine wave repeated at 1 kHz at a spatial average temporal average intensity of 30mW/cm2 with a pulsed width of 200 μs. After euthanasia, gross morphological evaluation was performed on 2-dimensional photographs and 3-dimensional virtual models of hemi mandibles by means of AutoCAD and Geomagic QUALIFY software, respectively. Then, tissue reactions of the condylar head were assessed in the middle and posterior regions in sagittal plane. Evaluation of the mineralization and microstructure properties of subchondral cancellous bone was carried out with microcomputed tomography (micro-CT) scanning. Qualitative and histomorphometric analysis was performed on condylar cartilage and subchondral bone following Alcian-Blue Pas and Goldner’s Trichrome staining. Vital flourochrome (calcein green) labeling was also utilized to determine the amount of endochondral bone growth in a time interval during the experimental period. The two and three dimensional linear measurements of the mandibles were indicative of identical gross features of treated samples to untreated ones. However, a slight statistically non-significant increase in the condyle’s growth direction (backward/upward) was detected in LIPUS group and the condylar cartilage was consistently thick and translucent in the most superior (middle) area in almost all experimental samples. In addition, comparing the average three-dimensional (computer generated) virtual models from experimental and control groups in the form of a 3-D deviation map was suggestive of enhanced periosteal bone apposition at the site of LIPUS application. Histomorphometric and micro-CT analysis revealed that slight but statistically significant changes occurred at both cartilage and subcondral cancellous bone levels. In the posterior region, augmented total fibrocartilage, fibrous, and prechondroblastic layer thickness as well as increased cell population in the latter layer were detected. In the middle region, thickness as well as cell population in the chondroblastic layer also showed significantly higher values in the experimental group compared to that of the control group. Moreover, in subchondral cancellous bone, bone remodeling activity and active bone formation was increased in the middle region, which was detected by decreased bone volume fraction and increased percentage of newly formed bone and remnants of calcifying cartilage. In addition, osteoid thickness in trabecular bone subjacent to cartilage bone junction was 37% higher in the LIPUS group than in the control group.This was more evident in the middle region. The lower values of bone mineral density, bone volume fraction, trabecular thickness, and degree of anisotropy as well as higher values of bone specific surface and trabecular number obtained by micro-CT analysis in the LIPUS group compared to that of the control group also supported histomorphometric results. The changes in subchondral cancellous bone in the posterior region followed relatively the same trend but they did not reach a statistically significant level. Even though we had technical difficulty in vital staining, the results were suggestive of a greater amount of endochondral bone formation in the experimental group compared to that of the control group. In conclusion, LIPUS may stimulate both chondrogenesis and osteogenesis in young adult rat mandibular condyle and enhance endocondral bone formation and subcondral trabecular bone remodeling. This response is region specific probably due to differences in intrinsic maturity of the condylar cartilage in different regions (Middle versus Posterior).The middle region of the mandibular condyle maintains growth cartilaginous characteristic into the later stages and so it might be more responsive to LIPUS stimuli.

• Subjects / Keywords

  • Mandibular Condyle
  • Adults
  • LIPUS

• Graduation date

  Spring 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3G44J28G

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.